1. Field of the Invention
The present invention pertains to intrusion detection systems. In particular, the system according to the present invention is intended to detect intrusions across an extended line of many feet in length, such as the perimeter of a restricted area.
2. Description of the Prior Art
Intrusion detection systems utilizing either a series of seismic point sensors or a single magnetic line sensor have been used in the prior art. An example of a system using geophones as seismic point sensors is shown in U.S. Pat. No. 3,818,471, wherein a plurality of geophones are required to define a line across which intrusions are being monitored. Although such systems are useful for some applications, they are not able to distinguish effectively between a valid crossing and signals generated by other disturbances. This inability to adequately distinguish between actual intrusions and other disturbances may result in an undesirably large number of false alarms.
U.S. Pat. No. 3,846,790, discloses an intrusion detection system which utilizes a line sensor capable of detecting both magnetic and seismic disturbances. By using both the magnetic and seismic information from the line sensor, the system is able to decrease the probability of false alarms while at the same time increasing the probability of detecting actual intrusions. While this system is a substantial improvement over the prior art in its ability to decrease the number of false alarms, further improvement for some applications is desirable.